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SubjectRe: [PATCH 4/4] block: Optionally snapshot page contents to provide stable pages during write
On Mon, Dec 17, 2012 at 12:13:36AM +0800, Zheng Liu wrote:
> On Thu, Dec 13, 2012 at 12:08:11AM -0800, Darrick J. Wong wrote:
> > diff --git a/mm/bounce.c b/mm/bounce.c
> > index 0420867..fa11935 100644
> > --- a/mm/bounce.c
> > +++ b/mm/bounce.c
> > @@ -178,6 +178,38 @@ static void bounce_end_io_read_isa(struct bio *bio, int err)
> > __bounce_end_io_read(bio, isa_page_pool, err);
> > }
> >
> > +#ifdef CONFIG_NEED_BOUNCE_POOL
> > +static int might_snapshot_stable_page_write(struct bio **bio_orig)
> > +{
> > + return bio_data_dir(*bio_orig) == WRITE;
> > +}
> > +
> > +static int should_snapshot_stable_pages(struct page *page, int rw)
> > +{
> > + struct backing_dev_info *bdi;
> > + struct address_space *mapping = page_mapping(page);
> > +
> > + if (!mapping)
> > + return 0;
> > + bdi = mapping->backing_dev_info;
> > + if (!bdi_cap_stable_pages_required(bdi))
> > + return 0;
> > +
> > + return mapping->host->i_sb->s_flags & MS_SNAP_STABLE &&
> > + rw == WRITE;
> > +}
> > +#else
> > +static int might_snapshot_stable_page_write(struct bio **bio_orig)
> > +{
> > + return 0;
> > +}
> > +
> > +static int should_snapshot_static_pages(struct page *page, int rw)
> ^^^^^^
> It should be _stable_.

Good catch! Thank you!

--D
>
> Regards,
> - Zheng
> > +{
> > + return 0;
> > +}
> > +#endif /* CONFIG_NEED_BOUNCE_POOL */
> > +
> > static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> > mempool_t *pool)
> > {
> > @@ -192,7 +224,8 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> > /*
> > * is destination page below bounce pfn?
> > */
> > - if (page_to_pfn(page) <= queue_bounce_pfn(q))
> > + if (page_to_pfn(page) <= queue_bounce_pfn(q) &&
> > + !should_snapshot_stable_pages(page, rw))
> > continue;
> >
> > /*
> > @@ -284,7 +317,8 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
> > * don't waste time iterating over bio segments
> > */
> > if (!(q->bounce_gfp & GFP_DMA)) {
> > - if (queue_bounce_pfn(q) >= blk_max_pfn)
> > + if (queue_bounce_pfn(q) >= blk_max_pfn &&
> > + !might_snapshot_stable_page_write(bio_orig))
> > return;
> > pool = page_pool;
> > } else {
> --
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